This arena lies within the Highlands of Outworld. The Portal remains still, with the exception of lightning striking in the center. This gateway is very unstable and unpredictable. Shadow Priests stand guard as watchers. Where the portal actually leads to still remains a mystery. In Mortal Kombat: Shaolin Monks, the Portal is the basis of several areas in Outworld (essentially its hub). Each of these areas are generally guarded by two Shadow Priests that must be defeated before the bridge to the portal will appear.
Mortal Kombat II
In the Sega Genesis version of Mortal Kombat II, there was a blue palette-swapped version of the Portal that was used to fight the secret characters Jade, Smoke and Noob Saibot instead of fighting in Goro's Lair.
The MKII version of the Portal also reappeared in Mortal Kombat Trilogy with an added pagoda-style temple on each end of the arena. The towers from the Hidden Portal can be seen on one side of the arena (now filled with characters from MK1 to MK3 on separate towers if observed closely), with the Portal arena on the other.
Mortal Kombat 3
In Mortal Kombat 3, the Portal reappears again as the stage where one confronts Smoke. It has however, gone under a slight change. It uses the floor from the Pit III and several tournament ladders are strewn across the landscape before the portal.
In its updated version in Ultimate Mortal Kombat 3, a light blue version of the arena appears as Scislac Busorez (renamed Lost Bridge in the N64 version of Mortal Kombat Trilogy) where the opponent faces off against secret characters, namely Classic Sub-Zero, for whom the arena is named after, albeit scrambled. The arena is unlocked in the normal arena scroll after the player unlocks all of the secret characters.
Mortal Kombat: Deception
In Mortal Kombat: Deception, the Portal appears as a combination of its II and 3 incarnations. One side displays the MK3 version (complete with filled ladder spaces using portraits from MK1 to MK4) and the other shows its MKII incarnation. Unlike MKII, five Shadow Priests will watch battles between players there. Chose Your Destiny towers can also be seen. This version is very similar to the Hidden Portal.
Mortal Kombat: Shaolin Monks
The Portal is the third stage of the game Mortal Kombat: Shaolin Monks and is accessed after having removed the Tarkata hordes from the Wu Shi Academy at this stage players can access a number of portals and are sent to certain points in the game where they must stop the warriors of Shang Tsung. The main enemies of this stage are the already-known Shadow priests, who use their dark magic to try to put an end to the players as well as attempting to stop Liu Kang and Kung Lao's access to any portal. At this stage of the game you can access other areas found in the same way. To get there you have to be very fast as far as combat is concerned since Shadow Priests will have the help of other killers like the Tarkata or other enemies such as the Demon Captain and other guards of Shao Kahn.
Mortal Kombat: Armageddon
In Mortal Kombat: Armageddon, the Portal receives another visual design and is now multi-tiered. The default tier resembles a worn down version of the the Evil Tower whilst the lower one features a portal in the background and is used as a deathtrap. Those unfortunate enough to get knocked into the portal will have their bodies ripped apart and crushed as their pieces are sucked further in, a reference to Raiden having warned Liu Kang and Kung Lao about unstable portals in Mortal Kombat: Shaolin Monks.